1. Field of the Invention
The present invention relates to a switching device and, more particularly, to a switching device such as an electromagnetic relay, a switch or a timer for switching an electric current.
2. Description of the Related Art
As the switching device for closing the DC electric current, there is a closed type relay device, as disclosed in JP-T-9-510040, for example) in the prior art.
As a coil portion 40 is magnetized and demagnetized, more specifically, a plunger 9 is brought into and out of contact with a core center 4 so that an armature assembly 8, as integrated with the plunger 9, and an armature shaft 10 are slit in the axial direction to bring a moving contact disc 21 into and out of contact with stationary contacts 22 and 22.
In the closed type relay device, the arc current, as produced when the moving contact disc 21 is brought into and out of contact with the stationary contacts 22 and 22 is broken by extending it outward with the magnetic force of a permanent magnet 33 packaged in the stationary contact 22.
However, a predetermined extension is needed for extending and breaking the arc current. Therefore, the closed type relay device cannot reduce the size of a structure 3 housing the stationary contact 22 and the moving contact disc 21, so that its size reduction is limited.
Even if the directivity for mounting the permanent magnet 33, i.e., the so-called “polarity” is arranged conforming the specifications, according to the aforementioned closed type relay device, the arc current produced is extended inward when the current flow direction in use is reversed from that of the specifications, so that it is difficult to break. When an AC current is to be switched by the closed type relay device, moreover, the AC current flow direction periodically changes so that the arc current produced at the switching time is extended not only outward but also inward. As a result, the arc current produced cannot be easily broken in a reliable manner, thus causing a problem that the reliability of the switching characteristics is low.